here is how to do a really strong magic effect using a deck of cards and a knife.
things you need:
standard deck of cards
neodymium magnet, (extremely strong magnet found in magic stores or online shopping)
Step 1: Setup
tape the magnet to bottom card
ask spectator to choose a card
cut the deck and put spectators card in middle of pack under the magnet.
because of the magnet you can create the illusion that you magically levitate half the cards cutting to their card as shown above.